Analytical devices suitable for use in the home, clinic or doctor's office, which are intended to give an analytical result that is rapid and requires a minimum degree of skill and involvement from the user are well known. Such test devices are common, for example, in home pregnancy tests and blood glucose tests.
Typically, a diagnostic strip is provided that contains reagent chemistry that forms a color or other indication of the presence of the analyte in a sample. The strip is read visually or by a meter.
Many rapid diagnostic tests use a process known as solid phase immunoassay immunochromatography. In a typical process, a sample is deposited on a paper strip and is moved by capillary action from one end to the other. The sample dissolves or solubilizes dried chemical reagents and immunologic reagents attached to particles such as colloidal gold. The suspension of colloidal gold particles moves across the paper strip by capillary action. The colloidal gold typically has antibodies, coated thereon or attached thereto, that bind with the test drug. A band of immobilized drug is provided. When colloidal gold particles move into this band, if antibodies have not bound with some test drug present in the specimen, the particles will bind with the drug immobilized in the band region and a color will be produced. If drug from the specimen sample has bound to the antibody, then the colloidal particles will migrate through the band region without forming a color product. Typically, such tests are complete in about five to ten minutes.
U.S. Pat. No. 5,656,503 describes a test device useful in pregnancy testing. A hollow casing is constructed of moisture-impervious solid material, such as a plastic, and contains a dry porous carrier, which communicates indirectly with the exterior of the casing via a bibulous sample receiving member that protrudes from the casing. The test sample is applied to the receiving member and permeates therefrom to the porous carrier. The porous carrier contains a first zone having a labelled specific binding reagent that is freely mobile within the carrier when in a moist state. The mobility is facilitated by a sugar in an amount effective to reduce interaction between the test strip and the labelled reagent. The carrier also has a second zone, spatially distinct from the first zone, containing an unlabelled specific binding reagent for the same analyte, which is permanently immobilized on the carrier and, therefore, is not mobile in the moist state. The two zones are arranged such that the liquid sample can permeate first into the first zone and then into the second zone. An aperture is provided in the casing to observe the extent to which labelled reagent becomes bound in the second zone.
U.S. Pat. No. 5,609,160 describes a collection device and package including a reagent strip having a testing portion that contains an absorbent cotton pad. The pad may be placed in the mouth to collect an oral fluid sample. A plastic frame surrounds the pad to help hold the fluid thereon. The testing strip contains at its opposite end a sealing mechanism for sealing engagement with a preservative pouch, and an oversized handle with a patient identifying mechanism. The preservative pouch contains a pair of seals. The first seal, located proximately to the user, enables a preservative that is maintained within the pouch to be sealed during shipment of the pouch to the user. Thereafter, the user punctures the first seal upon placement of the reagent pad into the pouch. The sealing mechanism contained on the reagent pad then seals the at the opening in the pouch to maintain the reagent pad in sealing engagement with the pouch. At its distal end, the pouch contains a second sealing mechanism. This sealing mechanism helps to protect the preservative as well as the oral sample within the pouch during shipment from the user to a testing laboratory. A chemical that will change color when sufficient oral fluid is taken up by the pad is coated on the pad.
Amperometric assay is another approach to the rapid assay of analytes in biological fluids. Such assays use electrodes to sense the presence of a redox mediator in the sample by various enzyme catalyzed reactions. U.S. Pat. No. 5,695,947 describes a device or biosensor for determining the presence of cholesterol in a sample. The cholesterol biosensor comprises a sensing electrode having a redox mediator dispersed in an electrically conductive graphite formulation, a reference electrode such as a standard silver--silver chloride or calomel electrode, and a membrane reagent strip containing reagents and enzymes with the strip in simultaneous contact with electrically conductive medium having the redox mediator dispersed therein and the reference electrode. The reagent strip has a second redox mediator system. An opening is provided to place a sample on the reagent strip. The liquid in the sample permeates the reagent strip to provide electrical connection between the reference electrode and the conductive medium.
Test membranes can exhibit problems of accuracy and repeatability of test results when the specimen sample is a viscous fluid, such as saliva. In such cases, the sample may not flow uniformly through the membrane to the testing zone. Thus, the visual detection may show uneven coloration. This can be difficult to interpret, even with a meter because the meter reading may differ depending upon the area of focus by the optics. In an electrochemical device, non-uniform concentrations can provide a conductive path that is not representative of the sample.
Thus, new and better diagnostic test membranes are desired, particularly for uniform and consistent results in economical rapid diagnostic testing.